Now that we have a jailbreak (developers only) for iPhone OS 4 Beta, and an upgraded version of Fuzzyband (Baseband downgrader).
Technically, iPhone 3G can now be unlocked on the latest iPhone OS 4 Beta, provided that you have one of those rare iPhone 3G’s with 05.08 bootloader that is downgradable to 05.13.03 baseband of OS 4 to 04.26.08 so that ultrasn0w can unlock it.
Here’s how you do it:
NOTE: I haven’t tested this on my iPhone 3G. This is only for iPhone 3G with 05.08 bootloader. Proceed only at your own risk.
Step 1: First follow the complete step by step guide posted here to jailbreak iPhone 3G on iPhone OS 4 Beta firmware.
Step 2: Using Fuzzyband, downgrade your baseband 05.13.03 to 04.26.08. Step by step instructions for downgrading baseband can be found here.
Step 3: Now start “Cydia” on your iPhone and touch on “Manage” tab on the bottom. Now touch on “Sources” as seen in the screenshot below:
Note: T-Mobile users should disable 3G before installing ultrasn0w.
Step 4: Touch on “Edit” and then on “Add”. You will be prompted to enter a url source as seen in the screenshot below. Type “http://repo666.ultrasn0w.com” and touch on “Add Source”.
Cydia will now automatically update your sources by following a series of automated steps.
Step 5: Once the repository has been added successfully, Search for “ultrasn0w” in Cydia and install this application.
Step 6: Now simply restart your iPhone.
If all goes well, you should now have an unlocked iPhone 3G running on iPhone OS 4 Beta.